Process for preparing jet fuel

ABSTRACT

PROCESS FOR PRODUCING JET FUEL IS PROVIDED COMPRISING HYDROCRACKING AT LEAST A PORTION OF A HYDROCARBON STREAM BOILING IN THE GAS OIL RANGE IN A HYDROCRACKING ZONE WHILE IN CONTACT WITH HYDROGEN AND A HYDROCRACKING CATALYST, FRACTIONATING THE EFFLUENT FROM THE HYDROCRACKING ZONE TO RECOVER A 320*/530* FVT JET FUEL PRECURSOR AND A 530* FVT+ BOTTOMS STREAM; HYDROGENATING SAID 320*/530* FVT PRECURSOR TO OBTAIN JET FUEL; CATALYTICALY CRACKING THE 530*FVT+ STREAM IN A CATALYTIC CRACKING ZONE TO OBTAIN AN ADDITIONAL 320*/530* FVT JET FUEL PRECURSOR STREAM AND GASOLINE; AND HYDROGENATING SAID JET FUEL PRECURSOR STREAM TO OBTAIN JET FUEL.

POST HYDROGENATION H UNIT FilGd April 13 J. BERNSTEIN ET AL rnocass FOR PREPARING JET 1mm.

FRACTIONATOR Aug. 7,

HYDROCRACKER LY ER INVENTIORS Jerom e B emstez/n ATTORNEYS 32075 30' FVT 530/ 700 F V T Walter We FRACTIONATOR '24- 7 4-- 5 30 FV T FLUID CATALYTIC CRACKER FEED Int. Cl. C10g 37/06 U.S. Cl. 208-61 11 Claims ABSTRACT OF THE DISCLOSURE Process for producing jet fuel is provided comprising hydrocracking at least a portion of a hydrocarbon stream boiling in the gas oil range in a hydrocracking zone while in contact with hydrogen and a hydrocracking catalyst, fractionating the effluent from the hydrocracking zone to recover a 320/530 FVT jet fuel precursor and a 530 FVT+ bottoms stream; hydrogenating said 320/530 FVT precursor to obtain jet fuel; catalytically cracking the 530 FVT+ stream in a catalytic cracking zone to obtain an additional 320/530 FVT jet fuel precursor stream and gasoline; and hydrogenating said jet fuel precursor stream to obtain jet fuel.

This invention relates to a process for preparing jet fuels. More particularly, this invention relates to a process for converting gas oils 'by hydrocracking and catalytic cracking to jet fuel, gasoline and valuable light ends products.

Although jet aircraft do not demand the high octane gasoline required by automobiles to suppress knock during the ignition cycle, jet aircraft nevertheless do demand a fuel stringently tailored to their peculiar combustion and handling environment.

The primary function of jet fuel is to burn completely with air and release heat energy to raise the temperature of the entire mass of air entering the turbine. To do this, the fuel must flow from tanks through metering devices to a nozzle, and there be injected under pressure into a fast flowing air stream. The injected fuel must vaporize completely and burn cleanly without leaving residues. The fuel must be fluid over a wide range of temperatures and, for maximum fuel economy, yield the highest possible heat units per pound.

Typical jet fuel specifications are set forth below in Table I. These specifications are the ASTM D1655 specifications for jet fuels designated Type A and Type A1, respectively.

Type A1 Gravity, API Heat content:

Aromatics, vol. percent max. Olefins, vol. percent max Smoke Point min Smoke-volatility index Corrosion, Cu strip, max. Water reaction, ml., max Existent gum, max. mgm./m1 Potential gum, max. mgrnJmL- Sulfur, wt. percent max.. Mercaptan, wt. percent ma Pour point, F. max- Freezing point, F. max- Viscosity, cs. max.l F Thermal stability test temp., F

AP in Hg, max Tube rating, max- Reid vapor pressure, p Flash cint, min Dist. P, min

10% min. evap. at F.) 20% min. evap. at FA 50% min. evap. at F.) 90% min. evap. at 1?.) FBI (final boiling point), F. max

United States Patent 3,751,360 Patented Aug. 7, 1973 Accordingly, it is an object of the present invention to provide a process for converting gas oils to high quality jet fuel.

It is another object of the present invention to provide a process for obtaining high quality jet fuel while simultaneously obtaining gasoline and valuable light ends products.

It is still another object of the present invention to provide a process for producing maximum quantities of jet fuel from gas oils with optimum utilization of hydrogen.

It is a still further object of the present invention to provide a process enabling the total conversion of gas oil to jet fuel, gasoline, and valuable light ends products by hydrocracking the gas oils to obtain partial conversion with subsequent catalytic cracking of the unconverted portion of the hydrocracked effluent.

These as well as other objects are accomplished by the present invention which provides a process for preparing jet fuel comprising hydrocracking a hydrocarbon boiling in the gas oil range in a hydrocracking zone while in contact with hydrogen and a hydrocracking catalyst, fractionating the hydrocracked efiluent to recover a 320/ 530 FVT (flash vaporization temperature) jet fuel precursor and a 530 FVT+ bottoms stream; hydrogenating said 320/S30 FVT precursor to obtain jet fuel; catalytically cracking said 530 FVT+ stream to obtain an additional 320/530 FVT jet fuel precursor stream, a 530/700 FVT light cat cycle oil and a 700/900 FVT heavy cat cycle oil; hydrogenating said jet fuel precursor to obtain jet fuel; recycling said light cat cycle oil to the hydrocracking zone and recycling said heavy cat cycle oil to extinction in said catalytic cracking zone.

The process of the present invention will be more completely understood from the drawing which illustrates a schematic arrangement of one method for carrying out the process of the present invention. The feedstock which can be a relatively high nitrogenand/or sulphur-containing feedstock such as, for example, a coker gas oil, catalytic cycle oil or a virgin gas oil feed, typically material boiling between 650 and l050 FVT is brought via line 2, mixed with recycle from line 6 and charged into a catalytic hydrocracker 10 containing one or more beds of hydrocracking catalyst. This unit accomplishes both hydrotreating and conversion of the feedstock in one operation.

Useful hydrocracking catalysts include (a) metal compounds contained on a porous non-zeolitic support, and (b) zeolite-containing catalyst having exchanged or deposited catalyst metals. Suitable catalyst materials falling within the first category are the oxides and/0r sulfides or molybdenum and/or tungsten, preferably composited with an iron group metal oxide and/or sulfide such as the oxides or sulfides of nickel and/or cobalt. Preferred catalysts of this type comprise sulfided composites of molybdenum oxide and nickel oxide supported on a porous, relatively noncracking carrier such as activated alumina or other difiicult to reduce refractory oxides having a Cat. Activity below about 25. When alumina is employed as the support, it may be promoted with phosphorous or a phosphorous containing compound such as phosphoric acid. The most preferred catalyst materials of this general type contain about 26 wt. percent nickel ble inorganic adjuvant upon which is deposited a minor proportion of a transition metal hydrogenation component. Desirably, the hydrogenation components are selected .from Group VIB and Group VIH metals and their oxides and sulfides. The porous adjuvant is preferably alumina, silica and mixtures thereof. The hydrogenation components are preferably employed in amounts varying from about 0.05% to 25% by wt. of the final catalyst composition, based upon free metal. More typically, the hydrogenation components are employed in amounts varying from about 0.1 to 10 wt. percent, based on free metal. The preferred catalyst species are a nickel exchanged hydrogen faujasite admixed with a major amount of alumina, the final catalyst also containing deposited nickel and/ or tungsten and/ or molybdenum metal or their oxides or sulfides.

The temperature within the hydrocracking unit can range from about 550 to about 850 F. and preferably range from about 650 to about 800 F. Pressure within the unit can range from about 500 to about 4000 p.s.i.g. and preferably ranges .from about 1000 to about 3000 p.s.i.g. The liquid hourly space velocity (LHSV) can range from about 0.2 to 10 and preferably ranges from about 0.5 to about 5. The hydrogen to hydrocarbon ratio ranges from about 1 to about 15M s.c.f./ b. and preferably ranges from about 2 to about 6M s.c.f./b. These conditions can be suitably adjusted and correlated so as to reduce the organic nitrogen content of the feed to below about 50 p.p.m. and preferably below about 10 p.p.m., and con comitantly to effect substantial desulfurization. Simultaneously, a portion of the hydrocarbon charge is converted into fractions boiling in the jet fuel range and lighter.

The total effluent .from the reactor 10 is passed into a heat exchanger or suitable cooling device 12. In the heat exchanger 12, the effluent is cooled to temperatures at which gaseous hydrogen can be separated from the liquid phase. The thus cooled efiluent is pased into a high pressure separator 14. The gaseous phase containing substantial amounts of hydrogen is removed and can be recycled to hydrocracker 10 through line 16. A liquid product from the high pressure separator 14 is passed through a depressurizing zone 18 and then charged to a suitable fractionating tower 20.

In the fractionator 20, liquid products are separated into suitable fractions. Light ends are removed and isobutane can be segregated as feedstock for subsequent alkylation. A C /320 FVT gasoline cut can be taken. A jet fuel cut boiling in the range of about 320/530 FVT can be taken and fed directly to a post-hydrogenation unit 22 wherein it can be saturated in a sweet (low sulfur) environment to meet jet fuel specifications. Hydrotreating the jet fuel in a sweet environment permits using catalysts which are highly active for aromatics saturation. A 530 FVT+ bottoms product from the fractionating column 20 consists of gasoline-free gas oil of excellent quality for catalytic cracking. This bottoms fraction can be withdrawn and preheated to somewhat below cracking temperatures in heater 24 and then transferred to a fluid catalytic cracker 26.

The preferred catalysts for use in the catalytic cracking unit are the crystalline aluminosilicate zeolite types. In general, the chemical formula of the anhydrous crystalline zeolites employed in the present invention expressed in terms of moles may be represented as:

wherein Me is selected from the group consisting of metal cations, hydrogen and ammonia, n is its valance and x is a number above 3, e.g., 4 to 14, preferably 4.5 to 6.5. The zeolites includes synthetic crystalline aluminosilicates, naturally occurring crystalline aluminosilicates and treated clays in which a substantial portion of the clay has been converted to crystalline zeolite. Synthetic materials include faujasites and mordenities. Natural materials are erionite, analcite, faujasite, phillipsite, clinoptilolite, chabazite, gmelinite, mordenite and mixtures thereof containing or treated to contain 595% crystalline aluminosilicate having an ordered structure. All or a portion of the cations of the zeolites such as sodium cations can be replaced with hydrogen ions, ammonium ions or metal cations such as rare earths, manganese, cobalt, zinc and other metals of Groups I to VIII of the Periodic Table. The catalyst can be one of the matrix types, i.e., one in which the zeolite crystals are coated with or encapsulated in a siliceous gel. Matrix catalysts contain 5-60%, preferably 5 to 20% crystalline zeolite. The catalyst is generally particulate in nature. The catalyst particles can be in the form of powder, granules or the like and may be of a size Within the range of from about 5 to about 250 microns. The catalyst particles should be sufficiently uniform in particle size to permit easy handling and avoid any tendency to classify in the circulating catalyst system.

Hot, regenerated catalyst is admixed with the bottoms product in the riser cracker 28 wherein it completes the preheating of the oil charge which was partially preheated in heater 24. As the catalyst is mixed with the oil in the riser cracker 28, the oil is flash vaporized and forms a suspended fluidized catalyst-hydrocarbon mixture which is forced through the riser cracker 28 into the dense bed of catalyst maintained within the reactor. In the reactor, the catalyst settles to a finite level and forms a fluidized bed the depth of which regulates the time of reaction and can be varied to provide the desired degree of cracking. This bed is maintained in a fluid, turbulent condition by the entering feed vapors which continuously pass upwardly, thereby effecting contact of oil with catalyst and producing a substantially uniform temperature in the range of about 900 to about 1100" F.

As cracking progresses, coke forms on the catalyst and reduces its acitivity. The spent catalyst laden with coke is continuously and automatically withdrawn through the stripping zone 30 at the bottom of the reactor where the absorbed and entrained feed vapors are stripped from the catalyst by countercurrent contact with a stripping gas admitted to the stripping zone through line 32. The stripped catalyst is picked up by a stream of air charged through line 38 and is carried into the regenerator wherein the carbon is burned 01f the catalyst at temperatures of about 1100 F. The entrained catalyst is removed via cyclone 40 and flue gas exits via stack 42. The hot regenerated catalyst leaves the bottom of the regenerator taking with it much of the heat of combustion and is recycled via line 44 to the catalytic cracking unit.

The cracked products together with the stripping gas pass through cyclone 45 which collects entrained catalyst and returns it to the dense bed. Upon leaving cyclone 45, vapors pass from the reactor to fractionator 46 which separates light ends and gasoline from the heavier components. The light products can be passed to a light end recovery unit wherein C and/or 0., boiling range material can be segreated for subsequent alkylation; A C 320 FVT gasoline fraction is recovered. A jet fuel fraction boiling in the range of about 320/530 FVT is passed to a post hydrogenation unit 22 wherein it is hydrogenated together with the similar fraction obtained directly from the hydrocracker in a sweet environment to meet jet fuel specifications. A light catalytic cycle oil cut boiling in the range of 530/700 FVT is recycled via line 6 to the feed stream being charged to the hydrocracking unit 10. The hydrocracking unit partially converts this fraction and saturates the remaining unconverted portion of the stream so that it can be effectively converted in the cat cracker 26. This 530/700 FVT distillate would be diflicult to convert by direct recycle to the cat cracker. A 700/900 FVT heavy catalytic cycle oil stream is recycled to extinction in the cat cracker. This stream is good cat cracking feed for making gasoline. Recycling it through the hydrocracking unit would require a great deal of extra hydrogen. Since the 530 FVT+bottoms stream from the hydrocracking unit which is fed to the cat cracker has essentially nil sulfur and very little nitrogen (less than 50 p.p.m.) a sweet jet fuel cut is thus obtained in the cat cracker. The sweet stream can be saturated in one step in the post hydrogenation unit. Thus, it becomes relatively inexpensive to make jet fuel from this cat distillate.

The overall yield pattern can be adjusted by varying operations in each unit and by varying the cut point between the distillate cuts in each unit. For maximum jet fuel yield, a relatively 'high conversion per pass would be employed in the hydrocracking unit with a relatively low conversion per pass in the cat cracker.

The foregoing invention is subject to many modifications apparent to those skilled in the art. For example, if desired, a heating oil or diesel product can be produced by withdrawing a 530/650 FVT cut from the cat cracker and/or from the hydrocracker. Additionally, it may be desirable to saturate the olefins in the C /320 FVT cat naphtha material to permit reforming a portion of this stock for octane improvement. This can be conveniently accomplished by introducing this material to the post hydrogenation unit. These as well as other modifications are intended to be included Within the scope of the present invention. What is claimed is: 1. Process for producing jet fuel comprising: hydrocracking a hydrocarbon feed stream boiling in the gas oil range in a hydrocracking zone while in contact with hydrogen and a hydrocracking catalyst;

fractionating the effluent from the hydrocracking zone to recover a 320/530 FVT jet fuel precursor, and a 530 FVT+ bottoms stream;

hydrogenating said 320/ 530 F V l precursor to obtainjet fuel;

catalytically cracking the 530 FVT+ stream in a catalytic cracking zone; fractionating the effluent of the catalytic cracking zone to obtain an additional 320/530 FVT jet fuel precursor stream and a 530/700 FVT fraction;

hydrogenating said additional jet fuel precursor stream to obtain jet fuel; and

recycling said 530"/700 FVT fraction to said hydrocracking zone.

2. Process as defined in claim 1 wherein the hydrocarbon starting stream boils in the range of about 650- 1050 F.

3. Process as defined in claim 1 wherein the hydrocracking zone is maintained at temperatures ranging from about 550 to about 850 F.

4. Process as defined in claim 1 wherein the hydrocracking zone is maintained at a pressure of from about 500 to about 4000 p.s.i.g.

5. Process as defined in claim 1 wherein the liquid hourly space velocity within the hydrocracking zone ranges from about 0.2 to about 10.

6. Process as defined in claim 1 wherein the hydrogen/ hydrocarbon ratio within the hydrocracking zone ranges from about 1 to about 15M s.c.f./ b.

7. Process as defined in claim 1 wherein the efliuent from the hydrocracking zone contains less than about 50 ppm. of organic nitrogen.

8. 'Process as defined in claim 1 wherein the jet fuel precursor streams are hydrogenated in a sweet environment.

9. Process as defined in claim 1 wherein a C /320" FVT gasoline cut is additionally recovered from the hydrocracking zone.

10. Process for producing jet fuel and gasoline comprising:

hydrocracking a hydrocarbon boiling in the gas oil range in a hydrocracking zone while in contact with hydrogen and a hydrocracking catalyst, fractionating the hydrocracked effluent to obtain gasoline, a 320/530 FVT jet fuel precursor and a 530 FVT+ bottoms stream; recovering said gasoline, and hydrogenating said 320/ 530 FVT precursor to obtain jet fuel;

catalytically cracking said 530 FVT+ stream in a fluid catalytic cracking zone to obtain an additional 320/ 530 FVT jet fuel precursor stream, gasoline, a 530/700 FVT light cat cycle oil and a 700/ 900 FVT heavy cat cycle oil;

hydrogenating said additional jet fuel precursor to obtain jet fuel;

recovering said gasoline; and

recycling said light cat cycle oil to the hydrocracking zone and recycling said heavy cat cycle oil to extinction in said fluid catalytic cracking zone.

11. Process as defined in claim 10 wherein a light ends stream is additionally recovered from both the hydrocracking and catalytic cracking zones.

References Cited UNITED STATES PATENTS 3,172,833 3/1965 Kozlowski et al. 208-58 3,184,402 5/19'65 Kozlowski et al. 2086l HERBERT LEVINE, Primary Examiner US. Cl. X.R. 208-58 

